Extracellular signal-regulated kinase 1/2 (Erk1/2) mitogen activated protein kinases (MAPKs) act within a conserved intracellular signaling pathway that canonically includes upstream Ras, Raf (MAP3K) and Mek (MAP2K) proteins. Prior AR49737 efforts demonstrated that Erk1/2 pathway signaling is integral to both epidermal homeostasis as well as to early tumor progression. We identified two Erk1/2-regulated long non-coding RNAs (lncRNAs) with essential roles in epidermal homeostasis, including, ANCR, which is required for epidermal progenitor tissue maintenance, and TINCR, which is required for epidermal differentiation. In searching for proteins that modulate Erk1/2 output, we targeted all Erk1/2 cascade-interacting proteins to identify IQGAP1 as the only MAPK scaffold that was dispensable for Erk1/2- mediated homeostasis but required for Erk1/2-driven tumor progression. This competing renewal will characterize how these Erk1/2 targets and interactors function. First, we will focus on new lncRNAs by defining their mechanistic actions in homeostatic maintenance. Anti-differentiation non-coding RNA (ANCR) is an Erk1/2-sustained, 855 bp lncRNA enriched in a variety of tissue progenitors that sustains the undifferentiated progenitor state. In contrast, terminal differentiation induced non-coding RNA (TINCR) is an Erk1/2- suppressed, differentiation-induced 3693 bp lncRNA containing 10 novel 25bp motifs that is required for epidermal differentiation. These two lncRNAs are each conserved and essential for epidermal homeostasis. Aim I will test the hypotheses that defining ANCR's RNA, protein, and genomic interactome will yield insight into its mechanism of action and that TINCR acts within a larger RNA-protein complex to prevent degradation of differentiation mRNAs. Second, we will define IQGAP1-dependent Erk1/2 targets in Erk1/2 driven early tumor progression as a means of separating Erk1/2 homeostatic signaling from its tumorigenic actions. During the prior cycle, we identified IQGAP1 as the sole protein among the many Erk1/2 MAPK cascade scaffolds that is required for Erk1/2-mediated carcinogenesis yet is dispensable for tissue maintenance. IQGAP1 can itself interact with numerous other tumor- enabling proteins in addition to Erk1/2, however, including b-catenin, Akt and Cdc42. Aim II will determine whether the Erk1/2 pathway is the dominant IQGAP1-interacting pathway in this setting and will characterize IQGAP1 targets in homeostasis and tumorigenesis. This proposal will define how the Erk1/2 MAPK pathway sustains homeostasis, yet also drives tumor progression, as a basis for new therapies for diseases of skin and other tissues.